a) Field of the Invention
The present invention relates generally to processes and apparatus for detection and measuring of chemically-bound sulfur, and more particularly, to the detection and measurement of sulfur combustion products which have been contacted by ozone to form chemiluminescent reaction products. The present invention also relates to improved processes and apparatus for enhancing the chemiluminescent detection of sulfur by the reduction of interfering compositions.
b) Discussion of the Prior Art
Numerous processes and apparatus have been devised for detecting and measuring chemical substances. Among detectors used to detect and measure fluids, whether from an independent source, or from the output of a gas chromatographic apparatus, are those using thermal conductivity, hydrogen flame ionization, electronic capture, alkaline flame ionization, and flame photometry. Of particular interest in recent years has been the sensitive and selected detection of sulfur compounds, both as a pollutant in the environment, and from other sources. The most widely utilized sulfur selective detector at the present time is the flame photometric detector (FPD). The FPD device and process is based on the fact that a hydrogen flame in the presence of air (oxygen) emits electromagnetic radiation, usually in the form of visible spectra light. In practice, a carrier fluid transporting a to-be-tested substance, for example an eluent separated from a sample by a chromatographic instrument, is mixed with an air stream (which may be oxygen enriched), and passed onto a hydrogen burner, or a burner in the presence of hydrogen. The resulting mixture contains hydrogen in excess of that required for complete combustion of the oxygen present. The luminous radiation caused by this combustion impinges or is reflected through an optical filter which has been selected according to the desired radiation wavelength of the substance to be measured. Subsequently, the light from the filter passes to a light detector, such as a photomultiplier tube. The photomultiplier tube produces a current which can be detected, measured, analyzed, recorded, and so on, to indicate the substance and the amount of the substance. Such an FPD system can be used as a specific selective detector and process for sulfur in sulfur-containing substances since a specific wavelength is emitted from the formation of molecular species of sulfur during the burning of the hydrogen flame. Such an FPD system is relatively sensitive and has been widely used, for example in pollution control and determination. However, the fundamental response of such FPD detectors to sulfur is not linear with respect to the concentration of the to be measured sulfur, and are difficult to calibrate with accuracy, especially for the measurement of low concentrations of sulfur. Another distinct problem with FPD devices is that numerous other components in the sample can interfere with accurate determination of sulfur.
Another approach to measuring sulfur-containing compounds in a fluid sample including includes the use of chemiluminescence detection schemes.
There remains a need for a process and device capable of measuring sulfur compounds accurately, quickly and in the low femtogram range without being sensitive to interference of other compounds and components of the sample being tested.